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Added item key check in internal each loop #35

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Added item key check in internal each loop #35

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10 changes: 10 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,16 @@ You can optimize initial display and scrolling when the height of items is known
</VirtualList>
```

## `itemKey`

Allow the internal loop to use a specific key in your data, to help invalidate list items properly if the data changes.

```html
<VirtualList itemKey="number" items={things} let:item>
<p>{item.number}: {item.name}</p>
</VirtualList>
```


## Configuring webpack

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12 changes: 11 additions & 1 deletion VirtualList.svelte
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
export let items;
export let height = '100%';
export let itemHeight = undefined;
export let itemKey = undefined;

let foo;

Expand Down Expand Up @@ -132,6 +133,15 @@
rows = contents.getElementsByTagName('svelte-virtual-list-row');
mounted = true;
});

// Use a key from the item data if specified
function getKey(row) {
if (itemKey && row.data.hasOwnProperty(itemKey)) {
return row.data[itemKey];
}

return row.index;
}
</script>

<style>
Expand Down Expand Up @@ -161,7 +171,7 @@
bind:this={contents}
style="padding-top: {top}px; padding-bottom: {bottom}px;"
>
{#each visible as row (row.index)}
{#each visible as row (getKey(row))}
<svelte-virtual-list-row>
<slot item={row.data}>Missing template</slot>
</svelte-virtual-list-row>
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